WO2019081331A1

WO2019081331A1 - Process for producing an aqueous acrylamide solution

Info

Publication number: WO2019081331A1
Application number: PCT/EP2018/078515
Authority: WO
Inventors: Michael Guenter BRAUN; Juergen Daeuwel; Peter OEDMAN; Diego GHISLIERI; Matthias Kleiner
Original assignee: Basf Se
Priority date: 2017-10-25
Filing date: 2018-10-18
Publication date: 2019-05-02
Also published as: WO2019081008A1; AR113389A1

Abstract

The present invention relates to methods for preparing aqueous acrylamide solutions having a low acrylic acid concentration, aqueous acrylamide solutions obtainable by such methods, and acrylamide homopolymers or copolymers obtainable by polymerizing such acrylamide. In addition, the present invention is also directed to methods for reducing the acrylic acid concentration of aqueous acrylamide solutions. The invention furthermore relates to a modular, relocatable bioconversion unit for manufacturing aqueous acrylamide solutions.

Description

Process for producing an aqueous acrylamide solution DESCRIPTION The present invention relates to methods for preparing aqueous acrylamide solutions having a low acrylic acid concentration, aqueous acrylamide solutions obtainable by such methods, and acrylamide homopolymers or copolymers obtainable by

polymerizing such acrylamide. In addition, the present invention is also directed to methods for reducing the acrylic acid concentration of aqueous acrylamide solutions. The invention furthermore relates to a modular, relocatable bioconversion unit for manufacturing aqueous acrylamide solutions.

BACKGROUND OF THE INVENTION Water-soluble, high molecular weight homo- and copolymers of acrylamide may be used for various applications such as mining and oilfield applications, water treatment, sewage treatment, papermaking, and agriculture. Examples include its use in the exploration and production of mineral oil, in particular as thickener in aqueous injection fluids for enhanced oil recovery or as rheology modifier for aqueous drilling fluids. Further examples include its use as flocculating agent for tailings and slurries in mining activities.

The raw material for polyacrylamide is typically the monomer acrylamide. In principal, there exist two different methods to produce acrylamide in industrial scales: Chemical synthesis and biological synthesis, wherein the biological synthesis methods are more and more on the rise due to milder reaction conditions and inherent process safety. Due to the milder reaction conditions, the absence of copper catalyst and the quantitative conversion of the nitrile, expensive downstream processing steps such as distillation or ion exchange can be avoided in the biological synthesis, thus resulting in cheaper plants with drastically reduced plant footprint.

However, it has been found that acrylic acid as side product may be present in the aqueous acrylamide solutions from bioconversion methods. This leads to reduced performance of the resulting acrylamide polymers, when using aqueous acrylamide solutions with acrylic acid impurities for the polymerization reactions. More specifically, the presence of acrylic acid can significantly impair the physical properties of the acrylamide polymer material, which e.g. leads to a reduced solubility and performance in various applications such as water treatment, paper making, oil recovery or mining. Therefore, monitoring the bioconversion process is necessary to ensure sufficient product quality with low amount of side products. This however requires many different equipment, tools and devices associated with the reactor in order to conduct a controlled bioconversion process. Several solutions have been suggested how to reduce the amount of side products in the bioconversion process from acrylonitrile to acrylamide and to reduce the complexity of the manufacturing and monitoring tools for the bioconversion reaction. EP1385972 discloses a method in which the biocatalyst is damaged as little as possible during the reaction, by-products are minimized and batch time is optimized. Therefore, a reactor with a pumping circuit is provided, in which a part of the reaction mixture is circulated by a pump and in which at least a heat exchanger is arranged. For a homogeneous content in the reactor a motor driven agitator is used. The reaction temperature is monitored by on-line measurements.

EP2267143 discloses a method for producing an amide compound from a nitrile compound using a biocatalyst that realizes low cost, energy saving and low

environmental burdens. For the method a reactor is used, wherein the nitrile compound is reacted with the biocatalyst to produce the amide compound under such stirring conditions that the stirring power requirement is in the range of 0.08 to 0.7 kW/m³.

EP2518154 discloses a method for producing acrylamide from acrylonitrile by a biocatalyst method, wherein both evaporation of acrylonitrile into a gas phase and damaging of a catalyst by stirring are prevented. In EP2518154 an acrylonitrile feed tube that feeds acrylonitrile into an aqueous medium while stirring said aqueous medium is disclosed.

EP2336346 discloses a method for producing acrylamide in presence of a biocatalyst in a reactor equipped with a tubular heat exchanger for removing reaction heat by maintaining the reaction temperature in a range of 5 to 20°C in order to prevent biocatalyst deactivation by heat.

JP2015057968 discloses a manufacturing apparatus which comprises a reaction vessel equipped with a stirrer and an external circulation line including a circulating pump and heat exchanger. A supply line for supplying the nitrile compound in the external circulation line is installed in the reaction vessel. Instead of feeding a nitrile compound directly into the reaction vessel, the nitrile compound is supplied to the external circulation line and then into the reaction vessel.

JP2014176344 discloses a method of producing an amide compound using a microorganism, wherein the heat removal is monitored. The reaction tank / production apparatus is equipped with a temperature control device for calculating the heat removal of the reaction heat. A heat exchanger is installed in an external circulation line. Further the use of stirrer and/or mixer is disclosed. WO2016/006556 describes a method for producing a compound using a continuous tank reactor which is provided with two or more reaction tanks for producing the compound and with a reaction liquid feeding pipe that feeds a reaction liquid from an upstream reaction tank to a downstream reaction tank. The tank reactor may be mounted in a portable container. The reaction liquid in the reaction vessel is agitated by stirring blades.

SUMMARY OF THE INVENTION In the light of the prior art the technical problem underlying the present invention was the provision of methods for preparing aqueous acrylamide solutions that overcome the disadvantages of those methods known in the art. The method for preparing aqueous acrylamide solutions of the present invention comprises a reactor with an external cooling circuit and no stirrer. Passing the aqueous reaction mixture through the temperature control circuit is sufficient to mix the aqueous reaction mixture. The obtained aqueous acrylamide solutions have a low amount of acrylic acid. The method for preparing an aqueous acrylamide solution enables high product quality and overcomes the disadvantages known in the art. The problem is solved by the features of the independent claims. Preferred

embodiments of the present invention are provided by the dependent claims.

The invention therefore relates to a method for preparing an aqueous acrylamide solution, said method comprising the following steps:

(a) adding the following components (i) to (iii) to a reactor to obtain a composition for bioconversion:

(i) a biocatalyst capable of converting acrylonitrile to acrylamide;

(ii) acrylonitrile;

(iii) water; and

(b) performing a bioconversion on the composition obtained in step (a) in a reactor; wherein the reactor comprises an external cooling circuit and wherein the reactor comprises no stirrer.

In a preferred embodiment, the acrylic acid concentration of the composition at the end of the bioconversion is 5000 ppm or less, preferably 2000 ppm or less, preferably 1500 ppm or less, preferably 1200 ppm or less, more preferably 1000 ppm or less, further preferably 750 ppm or less, even more preferably 500 ppm or less, most preferably 400 ppm or less, wherein indications of ppm each relate to weight parts and are each referred to the total weight of the composition at the end of the bioconversion.

In a preferred embodiment, the concentration of acrylamide in the obtained solution is in the range from 10% to 80%, is preferably in the range from 20% to 70%, preferably in the range from 30% to 65%, more preferably in the range from 40% to 60%, most preferably in the range from 45% to 55% by weight of acrylamide monomers. In a preferred embodiment, the concentration of acrylonitrile during the bioconversion should not exceed 6 % by wt. and may for example be in the range from 0.1 % by wt. to 6 % by wt., preferably from 0.2 % by wt. to 5 % by wt., more preferably from 0.3 % by wt. to 4 % by wt., even more preferably from 0.5 % by wt. to 3 % by wt., most preferably from 0.8 % by wt. to 2 % by wt., still most preferably from 1 % by wt. to 1 .5 % by wt., relating to the total of all components of the aqueous mixture.

In a preferred embodiment, the bioconversion in step (b) is performed at 5 °C to 40 °C for 10 minutes to 48 hours, preferably at 5 °C to 35 °C for 1 hour to 24 hours, more preferably at 15 °C to 30 °C for 10 min to 48 hours, most preferably at 18 °C to 28 °C for 3 hours to 15 hours.

In a preferred embodiment, the method is carried out using a semi-batch process. In a preferred embodiment, the acrylonitrile content and/or the acrylamide content during step (b) is measured using Fourier Transform Infrared Spectroscopy (FTIR).

In a preferred embodiment, measurement of heat-balance in step (b) is used for monitoring the bioconversion.

In a preferred embodiment, said biocatalyst encodes the enzyme nitrile hydratase.

In a preferred embodiment, the biocatalyst is Rhodococcus rhodochrous. In a preferred embodiment, the biocatalyst has been dried before being added to the reactor.

In a preferred embodiment, the biocatalyst has been dried using freeze-drying, spray drying, heat drying, vacuum drying, fluidized bed drying and/or spray granulation, wherein spray drying and freeze drying are preferred.

In a preferred embodiment, the reactor is a relocatable bioconversion unit.

In a preferred embodiment, the relocatable bioconversion unit comprises a double- walled reaction vessel having a volume from 10 m³ to 150 m³, means for mixing the reaction mixture and means for controlling the temperature of the reaction mixture.

In a preferred embodiment, the relocatable bioconversion unit comprises a frame, a double-walled reaction vessel mounted into the frame having a volume from 10 m³ to 150 m³, and an external temperature control circuit comprising at least a pump and a temperature control unit, wherein the reaction mixture is circulated by means of a pump from the reaction vessel into the temperature control unit and back into the reaction vessel, thereby simultaneously controlling the temperature and mixing the reaction mixture. In a preferred embodiment, the amount of reaction mixture cycled per hour through the temperature control circuit is from 100 % to 10000 %, preferably from 100 % to

5000 %, more preferably from 100 % to 2000 % and most preferably from 100 % to 1000 % of the total volume of the reaction mixture in the bioconversion unit.

In a preferred embodiment, the relocatable bioconversion unit is installed over a subterranean, oil-bearing formation or in a mining area.

The invention further relates to a reactor for manufacturing aqueous acrylamide solutions, wherein the reactor comprises an external cooling circuit and wherein the reactor comprises no stirrer.

In a preferred embodiment, the reactor is relocatable. In a preferred embodiment, the reactor for manufacturing aqueous acrylamide solutions comprises

o a relocatable storage unit for acrylonitrile,

o a relocatable bioconversion unit for hydrolyzing acrylonitrile in water in the presence of a biocatalyst capable of converting acrylonitrile to acrylamide, o optionally, a relocatable unit for removing the biocatalyst from an aqueous acrylamide solution.

o optionally, a relocatable storage unit for an aqueous acrylamide solution, o optionally, at least one relocatable unit for further processing an aqueous acrylamide solution.

In a preferred embodiment, a relocatable bioconversion unit is used at a fixed production facility.

The invention further relates to an aqueous acrylamide solution obtainable by the method according to the present invention.

In a preferred embodiment, the aqueous acrylamide solution contains 35 to 65 w/w % of acrylamide having an acrylic acid concentration of not more than 5000 ppm, preferably of not more than 1500 ppm, preferably of not more than 1000 ppm, more preferably of not more than 750 ppm, further preferably of not more than 500 ppm, most preferably of not more than 400 ppm, wherein indications of w/w % and ppm are each referred to the total weight of the solution, and ppm each relates to weight parts.

The invention further relates to an acrylamide homopolymer or copolymer obtainable by polymerizing the acrylamide of the aqueous solution according to the present invention.

In a preferred embodiment, the acrylamide homopolymer or copolymer has an acrylic acid content of 60,000 ppm or less, preferably of 20,000 ppm or less, more preferably of 10,000 ppm or less, and most preferably of 2,000 ppm or less, wherein the indications of ppm each relate to weight parts and are each referred to the total weight of the solid acrylamide homopolymer or copolymer.

In a preferred embodiment, the acrylamide copolymer is a cationic polyacrylamide.

In a preferred embodiment, the acrylamide copolymer is an anionic polyacrylamide. The invention further relates to the use of aqueous acrylamide solutions prepared according to the present invention for preparing aqueous solutions of acrylamide homopolymers or copolymers.

In a preferred embodiment, the aqueous polyacrylamide solutions according to the present invention are used for mining applications, oilfield applications, water treatment, waste water treatment, paper making or agricultural applications.

In a preferred embodiment, the method for preparing aqueous acrylamide solutions is used for reducing the acrylic acid concentration of aqueous acrylamide solutions.

DETAILED DESCRIPTION OF THE INVENTION

With regard to the invention, the following can be stated specifically: In a first aspect the invention relates to a method for preparing an aqueous acrylamide solution, said method comprising the following steps: a) adding the following components (i) to (iii) to a reactor to obtain a composition for bioconversion:

(i) a biocatalyst capable of converting acrylonitrile to acrylamide;

(ii) acrylonitrile;

(iii) water; and

b) performing a bioconversion on the composition obtained in step (a) in a reactor; wherein the reactor comprises an external cooling circuit and wherein the reactor comprises no stirrer.

Surprisingly, it was found that using a bioconversion reactor without a stirrer and an external cooling circuit results in an aqueous acrylamide solution with low amount of acrylic acid. With that the quality of the aqueous acrylamide solution is enhanced. Surprising was also that the mixing by the external cooling circuit (temperature control circuit) is sufficient, a stirrer is not needed and the product quality is even better without a stirrer. A further advantage of the present invention is that for example better subsequent products / polymers with lower amount of side products (acrylic acid) can be obtained. Having no stirrer in the bioconversion reactor offers the advantage of reduced engineering costs and less effort in process control. A further advantage is that with having difficult construction requirements for constructing a bio acrylamide production unit, with the present invention the bioconversion manufacturing unit can be built much simpler, with less effort and leads to a less complex bioconversion reactor construction. Based on the state of the art, if bioconversion reactors are not vertical designed but horizontal, this would require more stirrer. Advantageously, with the present invention and mixing by the external cooling circuit, stirrers are no longer needed. Surprisingly, the external cooling circuit is sufficient also with horizontal and/or vertical reactors to obtain a satisfactory mixture of the reaction composition / reaction mixture. It is possible to do mixing without a stirrer when producing acrylamide from acrylonitrile by a biocatalyst method.

Additionally, the reduced equipment complexity offers the possibility to conduct the bioconversion in a relocatable unit. Beneficial is in addition the possibility to avoid a purification and/or drying step, which will make the further processing of the aqueous acrylamide solution according to the present invention easier. Also, a direct use of the aqueous acrylamide solution at the site of further processing and/or the use of a subsequent polymer product at the site of application is possible.

Bioacrylamide

As used herein, the term "acrylamide" in the context of this invention means acrylamide that may be synthesized by partial hydrolysis of acrylonitrile using suitable catalysts. It is known in the art to use biocatalysts capable of converting acrylonitrile to acrylamide (often referred to as "bio acrylamide"). Pure acrylamide is solid. However, typically acrylamide according to the present invention is made by bio catalysis and is provided as aqueous solution, for example as aqueous solution comprising about 50 % by wt. of acrylamide. Solid acrylamide may be obtained from an aqueous solution of acrylamide by means of e.g. crystallization. Acrylamide obtained by means of biocatalysts may still comprise traces of the biocatalyst.

For the process according to the present invention an aqueous acrylamide solution is used which has been obtained by hydrolyzing acrylonitrile in water in presence of a biocatalyst capable of converting acrylonitrile to acrylamide. As will be detailed below, using biocatalysts for hydrolyzing acrylonitrile has significant advantages for the present invention.

Biocatalyst

As used herein, the term "biocatalyst" in the context of this invention means nitrile hydratase enzymes, which are capable of catalyzing the hydrolysis of acrylonitrile to acrylamide. The conversion of acrylonitrile to acrylamide using a biocatalyst may be called "bioconversion" or "bio-catalysis". Typically, nitrile hydratase enzymes can be produced by a variety of microorganisms, for instance microorganisms of the genus Bacillus, Bacteridium, Micrococcus, Brevibacterium, Corynebacterium, Pseudomonas, Acinetobacter, Xanthobacter, Streptomyces, Rhizobium, Klebsiella, Enterobacter, Escherichia Coli, Erwinia, Aeromonas, Citrobacter, Achromobacter, Agrobacterium, Pseudonocardia and Rhodococcus. WO 2005/054456 discloses the synthesis of nitrile hydratase within microorganisms and therein it is described that various strains of Rhodococcus rhodochrous species have been found to very effectively produce nitrile hydratase enzymes, in particular Rhodococcus rhodochrous NCI MB 41 164. Such microorganisms, suitable as biocatalyst for the enzymatic conversion of acrylonitrile to acrylamide, which are known for a person skilled in the art, are able to be applied according to the present invention. Additionally, the specific methods of culturing (or cultivation, or fermentation) and/or storing the microorganism as well as the respective sequences of polynucleotides which are encoding the enzyme, particularly the nitrile hydratase, are known in the art, e.g. WO 2005/054456, WO 2016/050816, and are applicable in context of the present invention. Within the present invention nitrile hydratase and amidase producing microorganisms may be used for converting a nitrile compound into the corresponding amide compound as it is described for example in WO 2016/050816. As used herein, the term "nitrile hydratase (NHase) producing microorganism" or "microorganism" or "biocatalysts" or the like in the context of this invention have the meaning to be able to produce (i.e. they encode and express) the enzyme nitrile hydratase (also referred to as, e.g., NHase) either per se (naturally) or they have been genetically modified respectively. Microorganisms which have been "genetically modified" means that these microorganisms have been manipulated such that they have acquired the capability to express the required enzyme NHase, e.g. by way of incorporation of a naturally and/or modified nitrile hydratase gene or gene cluster or the like. Produced products of the microorganisms that can be used in the context of the present invention are also contemplated, e.g. suspensions obtained by partial or complete cell disruption of the microorganisms.

The terms "nitrile hydratase (NHase) producing microorganism" or "microorganism" or "biocatalysts" or the like, include the cells and/or the processed product thereof as such, and/or suspensions containing such microorganisms and/or processed products. It is also envisaged that the microorganisms and/or processed products thereof are further treated before they are employed in the embodiments of the present invention. "Further treated" thereby includes for example washing steps and/or steps to concentrate the microorganism etc. It is also envisaged that the microorganisms that are employed in the embodiments of the present invention have been pre-treated by a for example drying step. Also known methods for cultivating of the microorganisms and how to optimize the cultivation conditions via for example addition of urea or cobalt are described in WO 2005/054456 and are compassed by the embodiments of the present invention. Advantageously, the microorganism can be grown in a medium containing urea, acetonitrile or acrylonitrile as an inducer of the nitrile hydratase. Preferably, the biocatalyst for converting acrylonitrile to acrylamide may be obtained from culturing the microorganism in a suitable growth medium. The growth medium, also called fermentation (culture) medium, fermentation broth, fermentation mixture, or the like, may comprise typical components like sugars, polysaccharides, which are for example described in WO 2005/054489 and which are suitable to be used for the culturing the microorganism of the present inventions to obtain the biocatalyst. For storage of the microorganism, the fermentation broth preferably is removed in order to prevent putrefaction, which could result in a reduction of nitrile hydratase activity. The methods of storage described in WO 2005/054489 may be applied according to the present invention ensuring sufficient biocatalyst stability during storage. Preferably, the storage does not influence biocatalytic activity or does not lead to a reduction in biocatalytic activity. The biocatalyst may be stored in presence of the fermentation broth components. Preferred in the sense of the present invention is that the

biocatalyst may be stored in form of a frozen suspension and may be thawed before use. Further, the biocatalyst may be stored in dried form using freeze-drying, spray drying, heat drying, vacuum drying, fluidized bed drying and/or spray granulation, wherein spray drying and freeze drying are preferred.

The biocatalysts that are used according to the present invention can for example be cultured under any conditions suitable for the purpose in accordance with any of the known methods, for instance as described in the mentioned prior art of this

specification. The biocatalyst may be used as a whole cell catalyst for the generation of amide from nitrile. The biocatalyst may be (partly) immobilized for instance entrapped in a gel or it may be used for example as a free cell suspension. For immobilization well known standard methods can be applied like for example entrapment cross linkage such as glutaraldehyde-polyethyleneimine (GA-PEI) crosslinking, cross linking to a matrix and/or carrier binding etc., including variations and/or combinations of the aforementioned methods. Alternatively, the nitrile hydratase enzyme may be extracted and for instance may be used directly in the process for preparing the amide. When using inactivated or partly inactivated cells, such cells may be inactivated by thermal or chemical treatment.

In a preferred embodiment, the microorganisms are whole cells. The whole cells may be pre-treated by a drying step. Suitable drying methods and/or drying conditions are disclosed e.g. in WO 2016/050816 and WO 2016/050861 and the known art can be applied in the context of the present invention.

The microorganisms that are employed in the context of the present invention are in a preferred embodiment used in an aqueous suspension and in a more preferred embodiment are free whole cells in an aqueous suspension. The term "aqueous suspension" thereby includes all kinds of liquids, such as buffers or culture medium that are suitable to keep microorganisms in suspension. Such liquids are well-known to the skilled person and include for example storage buffers at suitable pH such as storage buffers which are used to store microorganisms, TRIS-based buffers, phosphate based buffers, saline based buffers, water in all quality grades such as distilled water, pure water, tap water, or sea water, culture medium, growing medium, nutrient solutions, or fermentation broths, for example the fermentation broth that was used to culture the microorganisms. During storage for example the aqueous suspension is frozen and thawed before use.

The biocatalyst may be provided as powder, as granulate or as aqueous suspension to the reactor for bioconversion. If provided as powder or granulate it is frequently advisable to prepare an aqueous suspension before adding the catalyst into the reactor / bioconversion unit. In an embodiment, the biocatalyst suspension may be conducted by suspending the biocatalyst powder in water in a vessel comprising at least a mixing device, for example a stirrer, one or more inlets for water, the biocatalyst and optionally further additives and one outlet for the biocatalyst suspension. The volume of the vessel may be for example from 0.1 m³ to 1 m³. The concentration of the biocatalyst in the aqueous biocatalyst suspension may be for example from 1 % to 30% by wt, for example from 5 to 15% by wt. relating to the total of all components of the aqueous suspension.

A biocatalyst suspension may be added directly to the bioconversion unit. In another embodiment, a concentrated suspension may be diluted before adding it to the bioconversion unit / reactor where the bioconversion takes place.

Bioconversion The term "bioconversion" as used herein in the context with any one of the methods of the present invention in general denotes a reaction, wherein acrylonitrile is converted to acrylamide in the presence of water and a biocatalyst. The acrylamide is dissolved in the water, such that by any one of the methods described and provided herein an aqueous acrylamide solution is formed. As used herein, the term "composition" includes all components present in the reactor, such as, for example, the biocatalyst, acrylonitrile, acrylamide and water.

Particularly, the bioconversion is performed by contacting a mixture comprising water and acrylonitrile with the biocatalyst. The term "contacting" is not specifically limited and includes for example bringing into contact with, mixing, admixing, shaking, pouring into, flowing into, or incorporating into. It is thus only decisive that the mentioned ingredients come into contact with each other no matter how that contact is achieved.

Therefore, in one embodiment the present invention comprises the following steps:

(a) Adding the following components (i) to (iii) to a bioconversion unit to obtain a composition for bioconversion:

(i) a biocatalyst capable of converting acrylonitrile to acrylamide;

(ii) acrylonitrile; (iii) aqueous medium; and

(b) performing a bioconversion on the composition obtained in step (a).

The addition of components (i) to (iii) in step (a) may take place in any order or sequence. Also preparing a pre-mix of some or all components (i) to (iii) is possible to obtain a composition for bioconversion according to step (a).

The bioconversion can for example be conducted under any conditions suitable for the purpose in accordance with any of the known methods, for instance as described in the mentioned prior art of this specification like e.g. WO 2016/050817, WO 2016/050819, WO 2017/055518.

When adding the biocatalyst to the reactor in any one of the methods of the present invention, the biocatalyst may be taken directly from the fermentation broth.

Alternatively, in accordance with any one of the methods described herein, the biocatalyst may have been dried before being added to the reactor. In this context the term "before" does not necessarily mean that the biocatalyst has been dried and is then directly added to the reactor. It is rather sufficient that the biocatalyst has undergone a drying step at any time before it is added to the reactor, independently of whether further steps between the drying and the addition are performed or not. As non-limiting examples, such further steps between the drying step and the addition to the reactor may be storage or reconstitution. However, it is also possible to add the biocatalyst to the reactor directly after drying. It is known from WO 2016/050816 that by using a biocatalyst, which has undergone a drying step, the concentration of acrylic acid in an aqueous acrylamide solution obtained by any one of the methods described herein is further reduced in comparison to the case that a biocatalyst is used which has not undergone drying before being employed in the bioconversion.

Regarding the drying method, in any one of the methods described and provided herein, a biocatalyst may be used which has been dried using freeze-drying, spray drying, heat drying, vacuum drying, fluidized bed drying and/or spray granulation. With this respect, spray drying and freeze drying are preferred, since in general by using a biocatalyst, which has been subjected to spray- or freeze drying, a higher reduction of the acrylic acid concentration in the obtained aqueous acrylamide solutions is achieved compared to employing a biocatalyst which has been dried using other methods.

According to any one of the methods of the present invention a dried biocatalyst may be added to the reactor. This means that the biocatalyst is added to the reactor in a dried form. In particular, the biocatalyst may have the form of a powder or a granule. As an alternative to adding a dried biocatalyst to the reactor, the dried biocatalyst may be reconstituted before being added to the reactor. For example, the biocatalyst may be reconstituted by suspending in an aqueous composition. With this respect, the aqueous composition may be water or a buffer. As a further alternative, a biocatalyst in form of a matrix bound microorganism may be added to the reactor. The conversion of acrylonitrile to the acrylamide may be carried out by any of a batch process and a continuous process, and the conversion may be carried out by selecting its reaction system from reaction systems such as suspended bed, a fixed bed, a fluidized bed and the like or by combining different reaction systems according to the form of the catalyst. Particularly, the method of the present invention may be carried out using a semi-batch process. In particular, the term "semi-batch process" as used herein may comprise that an aqueous acrylamide solution is produced in a

discontinuous manner. According to a non-limiting example for carrying out such a semi-batch process water, a certain amount of acrylonitrile and the biocatalyst are placed in the bioconversion unit. Further acrylonitrile is then added during the bioconversion until a desired content of acrylamide of the composition is reached. After such desired content of acrylamide is reached, the obtained composition is for example partly or entirely recovered from the reactor, before new reactants are placed therein. In particular, in any one of the methods of the present invention the acrylonitrile may be fed such that the content of acrylonitrile during step (b) is maintained substantially constant at a predetermined value. In general, in any one of the methods of the present invention the acrylonitrile content and/or the acrylamide content during step (b) may be monitored. Methods of monitoring the acrylonitrile contents are not limited and include Fourier Transform

Infrared Spectroscopy (FTIR). In another embodiment, the heat-balance of the reaction may be used for monitoring the process. This means that monitoring via heat-balance method takes place by measuring the heat energy of the system during bioconversion and by calculating the loss of heat energy during the reaction in order to monitor the process. In yet another embodiment, the biocatalyst is recovered from the reaction mixture after the bioconversion and re-used in a subsequent bioconversion reaction.

Although the conversion of acrylonitrile to the acrylamide may preferably be carried out at atmospheric pressure, it may be carried out under pressure in order to increase solubility of acrylonitrile in the aqueous medium. Because biocatalysts are temperature sensitive and the hydrolysis is an exothermic reaction temperature control is important. The reaction temperature is not specifically restricted provided that it is not lower than the freezing point of the aqueous medium. However, it is desirable to carry out the bioconversion at a temperature of usually 0 to 50°C, preferably 10 to 40°C, more preferably 15 to 30°C. It is possible that the temperature may vary over time during the bioconversion reaction. Further suitable conditions for the bioconversion according to the present invention are for example described in WO 2017/055518 and are preferably applicable for the method in a bioconversion unit of the present invention. Although the amount of biocatalyst may vary depending on the type of biocatalyst to be used, it is preferred that the activity of the biocatalyst, which is introduced to the reactor, is in the range of about 5 to 500 U per mg of dried cells of microorganism. Methods for determining the ability of a given biocatalyst (e.g. microorganism or enzyme) for catalyzing the conversion of acrylonitrile to acrylamide are known in the art. As an example, in context with the present invention, activity of a given biocatalyst to act as a nitrile hydratase in the sense of the present invention may be determined as follows: First reacting 100 μΙ of a cell suspension, cell lysate, dissolved enzyme powder or any other preparation containing the supposed nitrile hydratase with 875 μΙ of a 50 mM potassium phosphate buffer and 25 μΙ of acrylonitrile at 25°C on an Eppendorf tube shaker at 1 ,000 rpm for 10 minutes. After 10 minutes of reaction time, samples may be drawn and immediately quenched by adding the same volume of 1 .4% hydrochloric acid. After mixing of the sample, cells may be removed by centrifugation for 1 minute at 10,000 rpm and the amount of acrylamide formed is determined by analyzing the clear supernatant by HPLC. For affirmation of an enzyme to be a nitrile hydratase in context with the present invention, the concentration of acrylamide shall particularly be between 0.25 and 1.25 mmol/l - if necessary, the sample has to be diluted accordingly and the conversion has to be repeated. The enzyme activity may then be deduced from the concentration of acrylamide by dividing the acrylamide concentration derived from HPLC analysis by the reaction time, which has been 10 minutes and by multiplying this value with the dilution factor between HPLC sample and original sample. Activities >5 U/mg dry cell weight, preferably >25 U/mg dry cell weight, more preferably >50 U/mg dry cell weight, most preferably >100 U/mg dry cell weight indicate the presence of a functionally expressed nitrile hydratase and are considered as nitrile hydratase in context with the present invention.

It is preferred, that the concentration of acrylonitrile during the bioconversion should not exceed 6 % by wt. and may for example be in the range from 0.1 % by wt. to 6 % by wt, preferably from 0.2 % by wt. to 5 % by wt., more preferably from 0.3 % by wt. to 4 % by wt., even more preferably from 0.5 % by wt. to 3 % by wt., still more preferably from 0.8 % by wt. to 2 % by wt. and most preferably from 1 % by wt. to 1 .5 % by wt., relating to the total of all components of the aqueous mixture. It is possible that the concentration may vary over time during the bioconversion reaction. In order to obtain more concentrated solutions of acrylamide the total amount of acrylonitrile should not be added all at once but it should be added stepwise or even continuously keeping the abovementioned concentration limits in mind. The disclosure of WO 2016/050818 teaches a method of additional dosing of acrylonitrile, which is suitable to be used and applied in the present invention. The concentration of acrylamide in the obtained solution is in the range from 10% to 80%, preferably in the range from 20% to 70%, more preferably in the range from 30% to 65%, even more preferably in the range from 40% to 60%, most preferably in the range from 45% to 55% by weight, based on the complete weight of the reaction solution. The reaction should be carried out in such a manner that the final

concentration of acrylonitrile in the final acrylamide solution obtained does not exceed 0.1 % by weight relating to the total of all components of the aqueous solution. Typical reaction times may be from 2 h to 20 h, in particular 4 h to 12 h, for example 6 h to 10 h. After completion of the addition of acrylonitrile, the reactor contents is allowed to further circulate for some time to complete the reaction, for example for 1 hour to 3 hours. The remaining contents of acrylonitrile should preferably be less than 100 ppm, based on the complete weight of the reaction solution.

The present invention further relates to aqueous acrylamide solutions obtainable or being obtained by any one of the methods described and provided herein.

An aqueous acrylamide solution, in particular an aqueous acrylamide solution obtainable or being obtained by any one of the methods described herein, may have an acrylic acid concentration of not more than 5000 ppm, preferably of not more than 1500 ppm, preferably of not more than 1000 ppm, more preferably of not more than 750 ppm, further preferably of not more than 500 ppm, even more preferably of not more than 300 ppm, still more preferably of not more than 200 ppm and most preferably of not more than 100 ppm, wherein indications of w/w % and ppm are each referred to the total weight of the solution, and ppm each relates to weight parts.

In any one of the aqueous acrylamide solutions, the acrylamide content and/or the acrylic acid concentration may be determined using HPLC. Preferably, an HPLC method is used as set forth below under the Examples. Bioconversion unit

The hydrolysis of acrylonitrile to acrylamide by means of a biocatalyst is performed in a suitable bioconversion unit (also called reactor). Suitable reactors for performing the bioconversion are known to the skilled artisan. Examples comprise vessels of any shape, for example cylindrical or spherical vessels, or tube reactors. Such reactors comprise particularly a pumping circuit comprising a heat-exchanger.

The bioconversion unit comprises a reaction vessel. The volume of the reaction vessel is not specifically limited and may range from 10 m³ to 150 m³, for example it may be about 20 m³ to 50 m³. Preferably, the reaction vessel should be double walled and should be horizontal. Such a construction avoids installing a pit for the collection of any leakage thereby ensuring an easier and quicker relocation of the reaction unit.

The bioconversion unit furthermore comprises means for controlling the temperature of the contents of the vessel. The hydrolysis of acrylonitrile to acrylamide is an exothermal reaction and therefore heat generated in course of the reaction should be removed in order to maintain an optimum temperature for bioconversion. The bioconversion unit furthermore usually comprises means for measurement and control, for example means for controlling the temperature or for controlling the pressure in the vessel.

For temperature control, the preferred bioconversion unit comprises an external temperature control circuit comprising a pump which pumps the aqueous reactor contents from the storage vessel through a heat exchanger and back into the storage vessel, preferably via an injection nozzle. In one embodiment, a separate, relocatable temperature control unit is used comprising pump and heat exchanger and which is connected with the bioconversion unit by pipes or flexible tubes. In a preferred embodiment, the temperature control circuit is integrated into the bioconversion unit. It may -for example- be located at one end of the unit next to the reaction vessel.

Surprisingly, it has been found, that the external temperature control circuit described above may also be used as means for mixing. The stream of the aqueous reaction mixture which passes through the temperature control circuit and which is injected back into the reaction vessel causes a circulation of the aqueous reaction mixture within the reaction vessel which is sufficient to mix the aqueous reaction mixture.

Preferably, no stirrer is used for the mobile bioconversion unit (i.e. reaction vessel). A stirrer is an additional mechanical device, which increases the technical complexity. When using the external temperature control cycle for mixing instead of a stirrer, the technical complexity can be reduced while still sufficient mixing during bioconversion can be ensured. Advantageously, without a stirrer a transportation step is easier, since no stirrer as additional technical component has to be removed before transportation of the mobile bioconversion unit. Further, a bioconversion unit without a stirrer offers more flexibility in form, shape, mechanical stability requirements and size for the

bioconversion unit. In particular, a horizontal set-up for the relocatable bioconversion unit can be realized easier without a stirrer and with mixing just via the external temperature control cycle. Adding acrylonitrile to the contents of the bioconversion unit may be performed in various ways. It may be added into the reaction vessel or it may be added into the temperature control circuit, for example after the pump and before the heat exchanger or after the heat exchanger. Injecting acrylonitrile into the temperature control circuit ensures good mixing of the reaction mixture with freshly added acrylonitrile. Preferably, acrylonitrile is added between pump and heat exchanger.

The amount of reaction mixture cycled per hour through the temperature control circuit is chosen such that sufficient mixing to the contents of the reactor as well as sufficient temperature control is achieved. In one embodiment, the amount of reaction mixture cycled per hour through the temperature control circuit may be from 100 % to 1000 % of the total volume of the reaction mixture in the bioconversion unit, in particular from 200 % to 1000 % and for example from 500% to 800%. Further possible is that the amount of reaction mixture cycled per hour through the temperature control circuit is from 100 % to 10000 %, preferably from 100 % to 5000 %.

Off-gases of the bioconversion unit may comprise acrylonitrile, acrylic acid and acrylamide. If necessary, according to the applicable rules such off-gases may be treated in a manner known in the art. For example, it may be possible to combust the off-gases. In one embodiment, all off-gases containing acrylonitrile, acrylic acid and acrylamide may be washed in a scrubber. The scrubber vessel may have a volume of 1 m³ to 100 m³, preferably a volume of 5 m³ to 100 m³, more preferably a volume of 10 m³ to 100 m³. It may be for example an ISOtank or relocatable storage vessel, preferably a double walled vessel. The scrubber water may preferably be collected in a tank and it may be re-used for next bio-conversion batch.

In another embodiment of the invention, for temperature control an external temperature control circuit, for example a cooling circuit is used, which comprises a pump which pumps the monomer from the storage vessel through a heat exchanger and back into the storage vessel.

The temperature control circuit may be a separate, relocatable temperature control unit comprising pump and heat exchanger and which is connected with the storage vessel by pipes or flexible tubes.

Modular, relocatable units

In one embodiment of the invention, aqueous solutions of bio acrylamide for use in the method according to the present invention may be manufactured at a fixed chemical plant, and may be shipped to another location for further processing. However, in another preferred embodiment of the present invention the manufacture of bio acrylamide may be performed in a modular, relocatable plant. Further preferred is for example a relocatable bioconversion unit, which can be combined with installations and/or units of a fixed chemical plant. Such combination of an existing plant with a modular, relocatable bioconversion unit offers flexibility in building a production line based on case specific needs. Such production line at a certain plant can be adjusted easily in case the production requirements change. The existing plant for example may be a fixed polymerization plant for polyacrylamide. So, the combination of a relocatable bioconversion unit offers the possibility of combining the manufacturing of bio acrylamide with units for further processing the acrylamide obtained from a relocatable bioconversion unit.

Particularly, in the light of the present invention it is possible to reduce the food print and complexity of the bio acrylamide manufacturing site. Having a bioconversion reactor without a stirrer / no agitating element reduces the engineering and processing control significantly. Therefore, in a preferred embodiment of the invention, the bioconversion unit / bioconversion reactor is a relocatable bioconversion unit. In one embodiment, the relocatable bioconversion unit is similar to the storage unit for acrylonitrile which also may be relocatable. Therefore it is possible to using largely the same equipment for storing the acrylonitrile and for the bioconversion step. This contributes to an economic process for manufacturing aqueous acrylamide solutions.

Due to the flexibility of having a relocatable bioconversion unit / bioconversion reactor without a mechanical stirrer / agitating device, it is possible to conduct the method for production of an aqueous acrylamide solution at the location where the further processing for example to the polymer polyacrylamide takes place. Manufacturing bio acrylamide directly at the site of further processing the acrylamide to for example polyacrylamides saves significant transport costs. Acrylonitrile is a liquid and may be transported as pure compound to the site of further processing. The molecular weight of acrylamide is about 34 % higher than that of acrylonitrile and acrylamide is typically provided as about 50 % aqueous solution. So, for a 50 % aqueous solution of acrylamide the mass to be transported is about 2.5-fold as much as compared to transporting pure acrylonitrile. Transporting pure, solid acrylamide means transporting only about 34 % more mass as compared to transporting pure acrylonitrile, however, additional equipment for handling and dissolving the solid acrylamide is necessary at the location where further processing takes place.

Furthermore, acrylamide is toxic and it is therefore an advantage to reduce the transportation distance or amount of acrylamide to be transported in order to reduce the risk of accidents when transporting acrylamide. A bioconversion according to the present invention in a relocatable bioconversion unit without a stirrer enables that advantage.

Acrylonitrile for bio-catalysis may be stored in one or more than one relocatable storage units. The storage unit comprises a storage vessel. The volume of the storage vessel is not specifically limited and may range from 50 m³ to 150 m³, for example it may be about 100 m³. Preferably, the storage vessel should be double walled and should be horizontal. Such a construction avoids installing a pit for the collection of any leakage thereby ensuring an easier and quicker relocation of the storage unit. Double- walled vessels may be placed on every good bearing soil. The storage unit furthermore comprises means for charging and discharging the vessel, means for controlling the pressure in the vessel, for example a valve for settling low-pressure or overpressure, and means for controlling the temperature of the acrylonitrile which preferably should not exceed 25°C. It furthermore may comprise means for measurement and control to the extent necessary. Examples of relocatable storage units comprise relocatable cuboid, storage tanks, preferably double-walled tanks. Further, any considerable form, shape and size of container is suitable and applicable for the storage and/or provision of acrylonitrile in the sense of the present invention. Particularly, standard iso-tanks are applicable for the storage and/or provision of acrylonitrile. Other examples comprise tank containers having a cuboid frame, preferably a frame according to the ISO 668 norm mentioned above and one or more storage vessels mounted into the frame. Such normed tank containers may be stacked and transported on trucks, railcars or ships in the same manner closed intermodal containers. Several different relocatable units may be bundled together to have a relocatable plant. Each relocatable unit may have certain functions. Examples of such relocatable units comprise units for storing and optionally cooling monomers and/or other raw materials, hydrolyzing acrylonitrile, mixing monomers, further processing the acrylamide to for example an aqueous polyacrylamide solution. Details will be provided below. For performing different processes, individual units may be connected with each other in a suitable manner thereby obtaining a production line. Also bundling a relocatable bioconversion unit with non-relocatable units is possible. "Relocatable unit" means that the unit is transportable basically as a whole and that is it not necessary to disassemble the entire unit into individual parts for transport.

Transport may happen on trucks, railcars or ships.

In one embodiment, such modular, relocatable units are containerized units which may be transported in the same manner as closed intermodal containers for example on trucks, railcars or ships. Intermodal containers are large standardized (according to ISO 668) shipping containers, in particular designed and built for intermodal freight transport. Such containers are also known as ISO containers. Such ISO containers may have external dimensions of a height of ~ 2.59 m, a width of ~ 2.44 m and a length of ~ 6.05 m. Larger ISO containers have external dimensions of a height of ~ 2.59 m, a width of - 2.44 m and a length of -12.19 m.

In another embodiment, the relocatable units are combined, thereby obtaining modular production plants for performing different processes according to the present invention. Such a modular construction using relocatable units provides the advantage, that the plants may be easily relocated if aqueous acrylamide solutions are no longer needed at one location but at another location.

At the site of manufacturing the aqueous acrylamide solution, at the site of further processing the acrylamide to obtain subsequent further products (e.g. polyacrylamide) and/or at the site of applying / using aqueous polyacrylamide solutions (e.g. for oilfield or mining applications) different relocatable units according to the present invention may be used and combined, for example:

o a relocatable storage unit for acrylonitrile,

o a relocatable bioconversion unit for hydrolyzing acrylonitrile in water in the presence of a biocatalyst capable of converting acrylonitrile to acrylamide, o a relocatable unit for removing the biocatalyst from an aqueous acrylamide solution,

o a relocatable storage unit for an aqueous acrylamide solution,

o relocatable units for further processing acrylamide with other water-soluble, monoethylenically unsaturated monomers different from acrylamide, o a relocatable unit for polymerization to obtain aqueous polyacrylamide solutions, and/or

o a relocatable unit for subsequent applications. Further processing of acrylamide

After having obtained the aqueous acrylamide solution further processing is possible. Further processing steps are for example removing the biocatalyst, drying the aqueous acrylamide solution and storing the dried acrylamide. Further processing steps are also mixing the aqueous acrylamide solution with other monomers in order to prepare a monomer solution which is suitable for a subsequent polymerization step to obtain homopolymers or copolymers deriving from acrylamide. Due to the benefits of a bioconversion reaction without a stirrer or without mechanical agitation device it is in particular possible to use the bioconversion reactor as make-up and/or storage device for a monomer solution, which could subsequently be used for a polymerization reaction. The different further processing steps may be performed at different locations. For example, each further processing step may be performed at a different location. Alternatively, all or some of the further processing steps may be performed at the same location, in particular at the location of use of either the aqueous acrylamide solution or at the location of use of the aqueous polyacrylamide solution. If performed at the same location, it is possible to connect the different modular units / modular reactors with each other as needed to perform for example the different steps comprising the bioconversion of acrylonitrile to acrylamide and subsequent preparation of a monomer solution and polymerization to obtain polyacrylamide directly after another.

Biomass removal

After bioconversion, the reaction vessel comprises an aqueous solution of acrylamide, which still comprises the biocatalyst suspended therein. The biocatalyst preferably becomes removed completely, essentially completely, or partially before

polymerization, however, removing the biocatalyst may not be absolutely necessary in every case. Whether it is necessary to remove the biocatalyst substantially depends on two factors, namely whether remaining biocatalyst negatively affects polymerization and/or the properties of the polyacrylamide obtained and/or the biocatalyst negatively affects the application of the obtained polyacrylamide solution. In one embodiment, at least 75 %, preferably at least 90 % by weight of the biomass -relating to the total of the biomass present- should be removed.

The method for removing the biocatalyst is not specifically limited. Separation of the biocatalyst may take place by for example filtration or centrifugation. In other embodiments, active carbon may be used for separation purpose. Procedurally, for removing the biocatalyst there are several options.

In one embodiment, the aqueous acrylamide solution comprising the biocatalyst is removed from the bioconversion unit, passed through a unit for removing the biocatalyst, and thereafter the aqueous acrylamide solution is filled into a suitable storage unit for acrylamide, for example a relocatable storage unit for acrylamide as described above.

In another embodiment, the aqueous acrylamide solution comprising the biocatalyst is removed from the bioconversion unit, passed through a unit for removing the biocatalyst and thereafter the aqueous acrylamide solution is filled directly into a monomer make-up unit for further processing, i.e. without intermediate storing in an acrylamide storage unit. In another embodiment, the aqueous acrylamide solution comprising the biocatalyst is removed from the bioconversion unit and is filled directly, i.e. without removing the biocatalyst, into the monomer make-up unit. In said embodiment, the biocatalyst is still present in course of monomer make-up for further processing and is removed after preparing an aqueous monomer solution.

In another embodiment it is even possible that the biocatalyst is not removed from the aqueous monomer solution and the biocatalyst is present during further processing. This non-removal of the biocatalyst is of advantage, because the processing step of removing the biocatalyst can be avoided which therefore leads to less process steps and makes the overall process simpler.

In another embodiment, the aqueous acrylamide solution comprising the biocatalyst is removed from the bioconversion unit, passed through a unit for removing the biocatalyst and thereafter filled back into the bioconversion unit. In order to ensure complete discharge of the bioconversion unit before re-filling it with the acrylamide solution, the unit for removing the biocatalyst should comprise a buffer vessel having a volume sufficient for absorbing the contents of the bioconversion unit.

The above-mentioned methods for biocatalyst removal are for example applicable for partwise and/or complete removal of the biocatalyst. Further, it is preferred, that the completely or partly removed biocatalyst may be reused for a subsequent

bioconversion reaction.

In a preferred embodiment, the aqueous acrylamide solution does no longer comprise the biocatalyst. However, in another embodiment the acrylamide solution still comprises the biomass. In said embodiment, the biocatalyst may be removed after preparing a aqueous monomer solution for further processing in the same manner as described above or it may not be removed. Criteria for deciding in which cases it may not be necessary to remove the biocatalyst have already been mentioned above. Aqueous monomer solution

In course of further processing, an aqueous monomer solution comprising at least water, acrylamide and optionally further water-soluble, monoethylenically unsaturated monomers is prepared. Basically, the kind and amount of water-soluble,

monoethylenically unsaturated comonomers to be used besides acrylamide is not limited and depends on the desired properties and the desired use of the aqueous solutions of polyacrylamides to be manufactured. Typical monomers fall under the definitions of neutral comonomers, anionic comonomers, cationic comonomers and/or associative comonomers, which an artisan knows from the state of the art and is also applicable in the context of the present invention.

As used herein, the term "water-soluble monomers" in the context of this invention means that the monomers are to be soluble in the aqueous monomer solution to be used for polymerization in the desired use concentration. It is thus not absolutely necessary that the monomers to be used are miscible with water without any gap; instead, it is sufficient if they meet the minimum requirement mentioned. It is to be noted that the presence of acrylamide in the monomer solution might enhance the solubility of other monomers as compared to water only. In general, the solubility of the water-soluble monomers in water at room temperature should be at least 50 g/l, preferably at least 100 g/l.

Depending on the chemical nature, the water-soluble, monoethylenically unsaturated monomers to be used may be provided as pure monomers or as aqueous solutions for further processing. It is also possible to provide a mixture of two or more water-soluble, monoethylenically unsaturated monomers, in aqueous solution or as pure monomers for further processing. Acrylamide and other water-soluble, monoethylenically unsaturated monomers such as ATBS, or DM3AQ, or mixtures thereof preferably may be stored in suitable storage units. The monomers may be provided by road tankers, ISO tanks, or rail cars and pumped into relocatable storage units.

The aqueous monomer solution for polymerization comprises water and 5 % to 45 % by weight, preferably 15 % to 45 % by weight of water-soluble, monoethylenically unsaturated monomers, relating to the total of all components of the aqueous monomer solution. The water-soluble, monoethylenically unsaturated monomers comprise at least acrylamide, preferably bio acrylamide which preferably is manufactured as described above without a stirrer and low acrylic acid content.

In one embodiment of the invention, the monomer concentration is from 8 % by weight to 24.9 % by weight, preferably from 15 % by weight to 24.9 % by weight, for example from 20 to 24.9 % by weight, relating to the total of all components of the aqueous monomer solution. The monomer concentration may be selected by the skilled artisan according to his/her needs. For preparing the aqueous monomer solution, the water- soluble, monoethylenically unsaturated monomers to be used are mixed with each other. All monomers and optionally additives may be mixed with each other in a single step but it may also be possible to mix some monomers and add further monomers in a second step. Also, water for adjusting the concentration of the monomers may be added. Water eventually used for rinsing lines in course of transferring the monomer solution into the polymerization unit, needs to be taken into consideration when adjusting the concentration.

Further additives and auxiliaries may be added to the aqueous monomer solution. Examples of such further additives and auxiliaries comprise bases or acids for adjusting the pH value. In certain embodiments of the invention, the pH-value of the aqueous solution is adjusted to values from pH 5 to pH 7, for example pH 6 to pH 7. Examples of further additives and auxiliaries comprise complexing agents, defoamers, surfactants, or stabilizers are known to a person skilled in the art. Preferably, it is also possible that the pH adjustment takes place in-situ, which means that via adjusting the acrylic acid content in the acrylamide solution and/or the aqueous monomer solutions the pH can be adjusted. This adjustment can take place directly without addition of further pH adjusting additives during the reaction. This adjustment can also take place directly during the reaction by addition of for example an acrylate buffer. Preferably, the preparation of the aqueous monomer solution is performed in a relocatable monomer make-up unit. In one embodiment, the monomer make-up may be the unit which is similar to the bioconversion unit as described above. Using largely the same equipment for storing acrylonitrile, for the bioconversion step and for further processing acrylamide contributes to an economic process for manufacturing aqueous acrylamide solutions. It is possible that the bioconversion unit may also be used for monomer make-up and has particularly no stirrer / no mechanical agitation device.

If the monomer make-up vessel is different to the bioconversion unit, it may be equipped with a stirrer for mixing the components of the aqueous monomer solution with each other. However, in the same manner as with the bioreactor, the external temperature control circuit may be used as means for mixing. The stream of the aqueous monomer mixture which passes through the temperature control circuit and which is injected back into the monomer make-up vessel causes a circulation of the aqueous reaction mixture within the reaction vessel which is sufficient to mix the aqueous reaction mixture.

Polymers

Furthermore, the present invention relates to an acrylamide homopolymer or copolymer obtainable or being obtained by polymerizing the acrylamide of the aqueous solution as described herein. With this respect, in case of a homopolymer the term "polymerizing" refers to a homopolymerization reaction, while in case of a copolymer the term

"polymerizing" refers to a copolymerization reaction. The homopolymerization or copolymerization may be performed using an aqueous acrylamide solution obtainable or being obtained by any one of the methods described herein. In particular, an aqueous acrylamide solution may be used, from which the biocatalyst has been separated prior to the polymerization. Alternatively, the acrylamide may have been isolated from the aqueous acrylamide solution before being subjected to

homopolymerization or copolymerization.

As used herein, the term "polyacrylamides" as used herein means water-soluble homopolymers of acrylamide, or water-soluble copolymers comprising at least 10 %, preferably at least 20 %, and more preferably at least 30 % by weight of acrylamide and at least one additional water-soluble, monoethylenically unsaturated monomer different from acrylamide, wherein the amounts relate to the total amount of all monomers in the polymer. Copolymers are preferred.

An acrylamide homopolymer or copolymer, in particular an acrylamide homopolymer or copolymer obtainable or being obtained by polymerizing the acrylamide of the aqueous solution as described herein, may have an acrylic acid content of 60,000 ppm or less, preferably of 20,000 ppm or less, more preferably of 10,000 ppm or less, and most preferably of 2,000 ppm or less, wherein the indications of ppm each relate to weight parts and are each referred to the total weight of the solid acrylamide homopolymer or copolymer.

High acrylic acid contents within acrylamide solutions can lead to reduced performance of the resulting polyacrylamide homopolymers and copolymers, especially for cationic polyacrylamide products, i.e. copolymers of acrylamide with cationic co-monomers. This is highly evident for cationic copolymers with low cationic co-monomer contents. Without being bound by any theory, molar equivalent amounts of anionic acrylic acid and the cationic co-monomers within the copolymer chain results in the generation of charge complexes. This can significantly impair the physical properties of the polyacrylamide material, reducing solubility and performance in applications such as water treatment, paper making, oil recovery or mining.

Regarding this impact of acrylic acid, the acrylamide homopolymer or copolymer described and provided herein is preferably a cationic polyacrylamide. As generally known to a person skilled in the art, the term "cationic polyacrylamide" denotes a copolymer which in addition to acrylamide monomers contains cationic co-monomers, such as, e.g., co-monomers which comprise quaternary ammonium groups. Particularly preferred is a cationic polyacrylamide having an acrylic acid content of 60,000 ppm or less, preferably of 20,000 ppm or less, more preferably of 10,000 ppm or less, and most preferably of 2,000 ppm or less, wherein the indications of ppm each relate to weight parts and are each referred to the total weight of the solid acrylamide homopolymer or copolymer.

In general, the acrylic acid content of any polymer or copolymer described herein may be determined using methods known in the art, e.g., NMR spectroscopy as described in European Polymer Journal (2007), 43(3): 824-834. Acrylamide homopolymers and/or copolymers are, for example, used in oilfield applications. In particular, use of acrylamide homopolymers and/or copolymers is made in tertiary oil recovery, which is also denoted as enhanced oil recovery. With this respect, in methods of tertiary oil recovery an aqueous solution of the polymer may be injected into the rock in order to promote oil displacement and thus increase the yield of crude oil. The present invention is therefore also related to an aqueous solution of any acrylamide homopolymer and/or copolymer described herein. As water for the aqueous solution seawater may be used. Although the invention has been described with respect to specific embodiments and examples, it should be appreciated that other embodiments utilizing the concept of the present invention are possible without departing from the scope of the invention. The present invention is defined by the claimed elements, and any and all modifications, variations, or equivalents that fall within the true spirit and scope of the underlying principles.

FIGURE

The invention is further described by the figures. These are not intended to limit the scope of the invention

Brief description of the figure

Figure 1 : Schematic representation of a bio acrylamide reactor

Detailed description of the figure

Figure 1 schematically represents an embodiment of the relocatable bioconversion unit with an integrated temperature control circuit. The bioconversion unit comprises a frame (10), a double-walled reaction vessel mounted into the frame comprising an outer wall (1 1 ) and an inner wall (12). Preferred volumes of the reaction vessel have already been mentioned. In other embodiments, the reaction vessel is self-supporting and there is no frame (10). The reaction vessel is filled with the reaction mixture. The bioconversion unit furthermore comprises an external temperature control circuit comprising at least a pump (13) and a temperature control unit (14). The reaction mixture is circulated by means of a pump (13) from the reaction vessel to the temperature control unit (14) and is injected back into the storage vessel, preferably via an injection nozzle (16). In the depicted embodiment, acrylonitrile is injected into the temperature control circuit thereby ensuring good mixing (15). It may be added before or after the temperature control unit. Figure 1 shows an embodiment in which acrylonitrile is added into the temperature control circuit between the pump and the heat exchanger. The stream of reaction mixture injected back into the reaction vessel causes a circulation of the reaction mixture in the reaction vessel which ensures sufficient mixing of the contents of the reaction mixture. No stirrer is installed. EXAMPLES

The invention is further described by the following examples. The examples relate to practical and in some cases preferred embodiments of the invention that do not limit the scope of the invention.

Examples

Examples 1 and 2: In a semi-batch process 2416 g of water and 20 g acrylonitnle (INEOS Koln HP) were placed in a glass reactor. The reactor was equipped with a pump loop containing a heat exchanger. In Example 1 the reactor was stirred. 0.91 g dried biocatalyst Rhodococcus rhodochrous, strain NCIMB 41 164, was suspended in 30 ml deionized water and added to the reactor, thereby starting the reaction. The contents of acrylonitrile and acrylamide were measured online during the bioconversion using Fourier Transform Infrared Spectroscopy (FTIR). The temperature was kept constant at 26°C during the reaction. 1533 g acrylonitrile (INEOS Koln HP) was added to the reactor with a controlled rate, so that the concentration of acrylonitrile was maintained at 0.8% (w/w) over the whole time of the bioconversion. After the feeding of acrylonitrile had stopped, the reaction was allowed to proceed until the acrylonitrile had been completely converted (< 100 ppm). At the end of the reaction 4 kg of an aqueous acrylamide solution having a content of 52 w/w % acrylamide and < 100 ppm acrylonitrile based on the total weight of the composition in the reactor was obtained.

Examples 3 and 4: In a semi-batch process 3686 g of water and 60 g acrylonitrile were placed in a glass reactor, equipped as in Examples 1 and 2 above. In Example 3 the reactor was stirred. 0.75 g dried biocatalyst Rhodococcus rhodochrous, strain NCIMB 41 164, was suspended in 30 ml deionized water and added to the reactor, thereby starting the reaction. The contents of acrylonitrile and acrylamide were measured online during the bioconversion using Fourier Transform Infrared Spectroscopy (FTIR). The temperature was kept constant at 23°C during the reaction. 1493 g acrylonitrile was added to the reactor with a controlled rate, so that the concentration of acrylonitrile was maintained at a certain setpoint during the bioconversion. During the first hour of the bioconversion, this setpoint was 2 % (w/w) acrylonitrile. After one hour, 0.3 g additional biocatalyst was suspended in 30 ml deionized water and added to the reactor, and the acrylonitrile concentration setpoint was decreased to 0.8 % (w/w). After the feeding had stopped, the reaction was allowed to proceed until the acrylonitrile had been completely converted (< 100 ppm). At the end of the reaction 4 kg of an aqueous acrylamide solution having a content of 52 w/w % acrylamide and < 100 ppm acrylonitrile based on the total weight of the composition in the reactor was obtained.

The following Table 1 shows the different examples of the method as described in the preceding paragraphs, wherein different conditions regarding stirring speed and recirculation rate were used during the bioconversion. Example Amount Stirrer Recirculation Reaction Acrylic acid

No. biocatalyst speed rate [L/h] time [h] concentration

[g] [RPM] [ppm]^*

1 0.91 250 160 5.73 482

2 0.91 — 40 5.49 307

3 0.75 + 0.3 250 40 7.35 278

4 0.75 + 0.3 — 40 6.97 172

— = no stirrer

^* determined using HPLC according to the method provided below

In the afore-mentioned examples, the final concentrations of acrylamide, acrylonitrile and acrylic acid in the obtained aqueous acrylamide solutions was determined using HPLC. The following conditions were applied in order to determine the contents of acrylamide, acrylic acid and acrylonitrile:

Column: Aqua C18, 250^*4.6 mm (Phenomenex)

Guard column: C18 Aqua

Temperature: 40 °C

Flow rate: 1 .00 ml/min

Injection volume: 1 .0 μΙ

Detection: UV detector, wavelength 210 nm

Stop time: 8.0 minutes

Post time: 0.0 minutes

Maximum pressure: 250 bar

Eluent A: 10 mM KH₂P0₄, pH 2.5

Eluent B: Acetonitrile

Gradient:

Fermentation broths, bioconversion mixtures

Sample is filtered through a 0.22 μηη prefilter

Retention time

[min]

Acrylamide 3.29

Acrylic acid 3.91

Acrylonitrile 4.35 Conclusion:

From table 1 it becomes obvious that without stirring the acrylic acid concentration in the aqueous acrylamide solution is lower than with a stirrer (speed of 250 RPM). This reduction of acrylic acid formation is reproducibly observed over different reaction conditions such as temperature and acrylonitrile feeding strategies. The reaction shows good reproducibility and full conversion of acrylonitrile to acrylamide even with reduced energy input due to no stirring. This results in the conclusion that passing the aqueous reaction mixture through the temperature control circuit is sufficient to mix the aqueous reaction mixture to produce an aqueous acrylamide solution with low acrylic acid concentration according to the present invention.

Claims

Claims:

Method for preparing an aqueous acrylamide solution, said method comprising the following steps:

(i) a biocatalyst capable of converting acrylonitrile to acrylamide;

(ii) acrylonitrile;

(iii) water; and

(b) performing a bioconversion on the composition obtained in step (a) in a reactor;

wherein the reactor comprises an external cooling circuit and wherein the reactor comprises no stirrer.

Method according to claim 1 , wherein the acrylic acid concentration of the composition at the end of the bioconversion is 1500 ppm or less, preferably 1200 ppm or less, more preferably 1000 ppm or less, further preferably 750 ppm or less, even more preferably 500 ppm or less, most preferably 400 ppm or less, wherein indications of ppm each relate to weight parts and are each referred to the total weight of the composition at the end of the bioconversion.

Method according to claim 1 or 2, wherein the concentration of acrylamide in the obtained solution is in the range from 20% to 70%, preferably in the range from 30% to 65%, more preferably in the range from 40% to 60%, most preferably in the range from 45% to 55% by weight of acrylamide monomers.

Method according to anyone of claims 1 to 3, wherein the concentration of acrylonitrile during the bioconversion should not exceed 6 % by wt. and may for example be in the range from 0.1 % by wt. to 6 % by wt., preferably from 0.2 % by wt. to 5 % by wt., more preferably from 0.3 % by wt. to 4 % by wt., even more preferably from 0.5 % by wt. to 3 % by wt., most preferably from 0.8 % by wt. to 2 % by wt., relating to the total of all components of the aqueous mixture.

Method according to anyone of the preceding claims, wherein the bioconversion in step (b) is performed at 5 °C to 40 °C for 10 minutes to 48 hours, preferably at 5 °C to 35 °C for 1 hour to 24 hours, more preferably at 15 °C to 30 °C for 10 min to 48 hours, most preferably at 18 °C to 28 °C for 3 hours to 15 hours.

6. Method according to anyone of the preceding claims, wherein the method is carried out using a semi-batch process.

7. Method according to anyone of the preceding claims, wherein the acrylonitrile content and/or the acrylamide content during step (b) is measured using Fourier Transform Infrared Spectroscopy (FTIR).

8. Method according to anyone of the preceding claims, wherein measurement of heat-balance in step (b) is used for monitoring the bioconversion.

9. Method according to anyone of the preceding claims, wherein said biocatalyst encodes the enzyme nitrile hydratase.

10. Method according to anyone of the preceding claims, wherein the biocatalyst is Rhodococcus rhodochrous.

Method according to anyone of the preceding claims, wherein the biocatalyst has been dried before being added to the reactor.

Method according to anyone of the preceding claims, wherein the biocatalyst has been dried using freeze-drying, spray drying, heat drying, vacuum drying, fluidized bed drying and/or spray granulation, wherein spray drying and freeze drying are preferred.

13. Method according to anyone of the preceding claims, wherein the reactor is a relocatable bioconversion unit.

14. Method according to anyone of the preceding claims, wherein the relocatable bioconversion unit comprises a double-walled reaction vessel having a volume from 10 m³ to 150 m³, means for mixing the reaction mixture and means for controlling the temperature of the reaction mixture.

15. Method according to anyone of the preceding claims, wherein the relocatable bioconversion unit comprises a frame, a double-walled reaction vessel mounted into the frame having a volume from 10 m³ to 150 m³, and an external temperature control circuit comprising at least a pump and a temperature control unit, wherein the reaction mixture is circulated by means of a pump from the reaction vessel into the temperature control unit and back into the reaction vessel, thereby simultaneously controlling the temperature and mixing the reaction mixture. 16. Method according to anyone of the preceding claims, wherein the amount of reaction mixture cycled per hour through the temperature control circuit is from 100 % to 1000 % of the total volume of the reaction mixture in the bioconversion unit. 17. Method according to anyone of the preceding claims, wherein the relocatable bioconversion unit is installed over a subterranean, oil-bearing formation or in a mining area.

18. Reactor for manufacturing aqueous acrylamide solutions according to the method of anyone of claims 1 to 17, wherein the reactor comprises an external cooling circuit and wherein the reactor comprises no stirrer. 19. Reactor according to claim 18, wherein the reactor is relocatable.

20. Reactor according to claim 19 comprising

o a relocatable storage unit for acrylonitrile,

o a relocatable bioconversion unit for hydrolyzing acrylonitrile in water in the presence of a biocatalyst capable of converting acrylonitrile to acrylamide, o optionally, a relocatable unit for removing the biocatalyst from an aqueous acrylamide solution,

o optionally, a relocatable storage unit for an aqueous acrylamide solution, and

o optionally, at least one relocatable unit for further processing an aqueous acrylamide solution.

21 . Reactor according to claim 19 for manufacturing aqueous acrylamide solutions according to the method of anyone of claims 1 to 17, wherein the relocatable reactor is used at a fixed production facility.

22. Aqueous acrylamide solution obtainable by the method according to anyone of claims 1 to 17. 23. Aqueous acrylamide solution according to claim 22, containing 35 to 65 w/w % of acrylamide having an acrylic acid concentration of not more than 1500 ppm, preferably of not more than 1000 ppm, more preferably of not more than 750 ppm, further preferably of not more than 500 ppm, most preferably of not more than 400 ppm, wherein indications of w/w % and ppm are each referred to the total weight of the solution, and ppm each relates to weight parts.

24. Acrylamide homopolymer or copolymer obtainable by polymerizing the

acrylamide of the aqueous solution according to anyone of claims 22 to 23. 25. Acrylamide homopolymer or copolymer according to claim 24, having an acrylic acid content of 60,000 ppm or less, preferably of 20,000 ppm or less, more preferably of 10,000 ppm or less, and most preferably of 2,000 ppm or less, wherein the indications of ppm each relate to weight parts and are each referred to the total weight of the solid acrylamide homopolymer or copolymer.

26. Acrylamide homopolymer or copolymer of claim 24 or 25, wherein the acrylamide copolymer is a cationic polyacrylamide.

27. Acrylamide homopolymer or copolymer of claim 24 or 25, wherein the acrylamide copolymer is an anionic polyacrylamide.

28. Use of aqueous acrylamide solutions prepared according to anyone of claims 1 to 21 for preparing aqueous solutions of acrylamide homopolymers or copolymers.

29. Use of aqueous solutions of acrylamide homopolymers or copolymers according to claim 28 for mining applications, oilfield applications, water treatment, waste water treatment, paper making or agricultural applications.

30. Use of the method according to anyone of claims 1 to 17 for reducing the acrylic acid concentration of aqueous acrylamide solutions.